Given, potential difference across diode,
VD=0.5V Maximum current in forward bias,
i=20mA=20×10−3A ⇒ Resistance of diode,
RD===25Ω Now, another resistance of
125Ω is connected with this diode in series.
So, effective resistance,
R=25+125=150Ω Clearly, maximum voltage to be used during forward bias,
V=iR=20mA×150Ω =3000mV=3.0V